Ion implantation is a process of depositing chemical species into a substrate by direct bombardment of the substrate with energized ions. In semiconductor manufacturing, ion implanters are used primarily for doping processes that alter the type and level of conductivity of target materials. A precise doping profile in an integrated circuit (IC) substrate and its thin-film structure is often crucial for proper IC performance. To achieve a desired doping profile, one or more ion species may be implanted in different doses and at different energy levels.
In an ion implantation process, an ion beam typically scans a wafer or substrate surface. As used hereinafter, “scanning” a wafer or substrate surface with an ion beam refers to the relative movement of the ion beam with respect to the wafer or substrate surface.
An ion beam is typically either a “spot beam” having an approximately circular or elliptical cross section or a “ribbon beam” having a rectangular cross section. For purposes of the present disclosure, a “ribbon beam” may refer to either a static ribbon beam or a scanned ribbon beam. The latter type of ribbon beam may be created by scanning a spot beam back and forth at a high frequency.
In the case of a spot beam, scanning of a wafer may be achieved by sweeping the spot beam back and forth between two endpoints to form a beam path and by simultaneously moving the wafer perpendicular to the beam path. Alternatively, the spot beam may be kept stationary, and the wafer may be moved in a two-dimensional (2-D) pattern with respect to the spot beam. In the case of a ribbon beam, scanning of a wafer may be achieved by keeping the ribbon beam stationary and by simultaneously moving the wafer across the ribbon beam. If the ribbon beam is wider than the wafer, a one-dimensional (1-D) movement of the wafer may cause the ribbon beam to cover the entire wafer surface. The much simpler 1-D scanning makes a ribbon beam a preferred choice for single-wafer ion implantation production.
However, just like spot beams, ribbon beams can suffer from intrinsic non-uniformity problems. A ribbon beam typically consists of a plurality of beamlets, wherein each beamlet may be considered, conceptually, as one spot beam. Though beamlets within a ribbon beam travel in the same general direction, any two beamlets may not be pointing in exactly the same direction. In addition, each beamlet may have an intrinsic angle spread. As a result, during ion implantation with a ribbon beam, different locations on a target wafer may experience different ion incident angles. Furthermore, beamlets may not be evenly spaced within the ribbon beam. One portion of the ribbon beam where beamlets are densely distributed may deliver a higher ion dose than another portion of the ribbon beam where beamlets are sparsely distributed. Therefore, a ribbon beam may lack angle uniformity and/or dose uniformity.
FIG. 1 depicts a conventional ion implanter system 100. As is typical for most ion implanter systems. The ion implanter system 130 may comprise an ion source 102 and a complex series of components through which an ion beam 10 passes. The series of components may include, for example, an extraction manipulator 104, a filter magnet 106, an acceleration or deceleration column 108, an analyzer magnet 110, a rotating mass slit 112, a scanner 114, and a corrector magnet 116. Much like a series of optical lenses that manipulate a light beam, the ion implanter components can filter and focus the ion beam 10 before steering it towards an end station 120.
An extraction electrode configuration, such as a ground electrode and a suppression electrode (not shown), may be positioned in front of the extraction manipulator 104. Each of the ground electrode and the suppression electrode have an aperture aligned with an aperture of the extraction manipulator 104 for extraction of a well-defined ion beam 10 from the ion source 102 for use in the ion implanter system 100.
The end station 120 supports one or more workpieces, such as workpiece 122, in the path of ion beam 10 such that ions of a desired species are implanted into the workpiece 122. The workpiece 122 may be, for example, a semiconductor wafer or other similar target object requiring ion implantation. The end station 120 may also include a platen 124 to support the workpiece 122. The platen 124 may secure the workpiece 122 using electrostatic or other forces. The end station 120 may also include a component (not illustrated) for moving the workpiece 122 in a desired direction. The end station 120 may also include additional components, such as automated workpiece handling elements for introducing the workpiece 122 into the ion implanter system 100 and for removing the workpiece 122 after ion implantation. It should be appreciated by those skilled in the art that the entire path traversed by the ion beam 10 is evacuated during ion implantation.
The ion implanter system 100 may also include a controller (not illustrated) to control a variety of subsystems and components of the ion implanter system 100. The ion implanter system 100 may also include a number of measurement devices, such as a dose control Faraday cup 118, a traveling Faraday cup 128, and a dose Faraday cup 126. These devices may be used to monitor and control ion beam conditions.
Although these additional components have been utilized in conventional ion implanters to improve either angle uniformity or dose uniformity of a ribbon beam, a more efficient solution has yet to be made available for providing ribbon beams that meet current dose and angle uniformity requirements for ion implantation production. For example, it is typically required that a ribbon beam should produce, in a wafer plane, a dose uniformity with less than 1% variations together with an angle uniformity with less than 0.50° variations. Such stringent uniformity requirements are becoming more difficult to meet since both types of uniformity may be elusive, especially in semiconductor manufacturing which require relatively high specificity and reliability.
In view of the foregoing, it may be understood that there are significant problems and shortcomings associated with current ion implantation technologies.